The present invention relates to a method and a machine for manufacturing gears and, in particular gears adapted to mesh with cylindrical pinions, of the type commonly known in the trade as face gears.
In the manufacture of face gears in general, it is known to use cutting machines which generate the teeth contours. However, the main disadvantage of these machines is that they make it difficult to work face gears of relatively small diameters and, at the same time, do not achieve satisfactory results in terms of either geometrical or dimensional precision or in terms of the finish of the worked surfaces.
In the manufacture of face gears, it is known to use disc tools which finish the flanks by working on the principle of generatrices and which have a peripheral cutting portion, the half-section of which, defined by a plane passing through the axis of rotation of the disc tool, has a cutting profile which is similar to the profile of the teeth of the aforesaid cylindrical pinion. During the cutting of the gear, the disc tool is driven in cycle in which it is reciprocated relative to the gear to be cut along a path perpendicular to the axis of rotation of the disc tool itself and is pivoted about an axis which is also perpendicular to the axis of rotation of the disc tool; at the same time as the disc tool is pivoted about this latter axis, the gear to be cut is rotated about its own axis in such a way that the ratio of the speed of pivoting of the disc tool to the speed of rotation of the gear being cut is always exactly the same as the transmission ratio resulting from the meshing of the gear with the pinion.
However, disc tools of the type just described have several disadvantages, all owing to the fact that their manufacture is relatively complex and very expensive. In fact, as is known, the theoretical contour of the gear teeth must be corrected in order to avoid relative slipping of the teeth of the gear and those of the pinion and, as the entire cutting operation is carried out without varying the ratio between the speeds of pivoting of the tool and rotation of the gear, the cutting portion of the disc tool needs to have a cutting profile which is different from the contour of the pinion teeth and, in particular, must be worked in such a way as to take account of the aforesaid contour correction, thus incurring not inconsiderable manufacturing costs and problems.